Much work has been done to study and imitate free swimming fish to try to effect a man-made free moving aquatic vehicle which approaches their propulsion efficiency, acceleration and maneuverability.
The MIT Robotuna (Scientific American, March, 1995), is a 49-inch long biologically inspired animated tow tank test platform model built to study swimming efficiency and how it relates to body kinematics. The body shape and flexibility mimics the yellowfin tuna, a fast swimming pelagic fish similar in shape and kinematics to the renowned bluefin tuna. Robotuna was meant to be flexible in that the design allows extreme body motion combinations well beyond the capabilities of a real tuna, enabling complete access to the swimming parameter space. The robot is comprised of six cable driven links which can be independently actuated. Each link is driven by a cable which runs via pulleys through the body and mast to a stepping motor mounted out of the water on the tow tank carriage.
The Robotuna was exercised in the MIT Ocean Engineering Testing Tank by prescribing a set of kinematic parameters (angular deflections of each joint, tow speed, jsi phase relationships) and measuring the net power transmitted to the linkages and the reaction force between the tuna and carriage.
The Robotuna is not a vehicle; it is a test platform. It does not contain pressure hulls, on-board electronics, power (such as batteries) or actuators. All of the body is actuated to some degree, either passively or actively, through the support structure that suspends it in the tank. There are sufficient number of links to adequately reproduce the required travelling sinusoidal wave for straight propulsion. The robot can bend into turning shapes but cannot turn or accelerate freely due to the fixed attachment to the towing carriage.
A later effort, Robopike (John Kumph, MIT B.S. thesis, May, 1996) is intended as a testbed for maneuvering and fast starting research. Unlike its carriage slaved predecessor, the Robopike will swim freely under radio control. The design is considerably smaller and simpler than the Robotuna to allow for packaging of all the actuators inside the body. The design was based on the actual size and form of a pike, a fish species renowned for fast acceleration and maneuvering.
Edge Innovations has built several aquatic animatronics robots for the motion picture industry. Apparently several models were built: a rubber dummy whale, a remotely operated whale with thrusters (propellers), and a remotely operated whale with hydraulic actuators (offboard hydraulic system). None are believed to be autonomous; Flipper was apparently a motor operated robot with unknown degrees of freedom and architecture. The Star Trek humpback whale was apparently a motor-operated whale with two degrees of freedom, one motor for up/down tail motion and one for side to side tail motion, all of which was encased in a urethane material to simulate the texture of a real whale. It is unclear from the limited literature/video available whether or not these robots contain pressure hulls. In the entertainment industry, animatronic robots are built for show only and do not contain the system elements necessary for an ocean-going vehicle (onboard power, actuation, control, payload, etc.). Work continues at MIT on Robopike. At Northeastern University there is work on an articulated testbed lamprey eel which is remotely operated, but has no pressure hull and no external body. The University of Tokai, Japan, Kato Lab has produced a Black Bass Robot remotely operated vehicle using pectoral fins for propulsion. There are no pressure hulls or onto board power. Motors provide pectoral fm movements. The Herriot-Watt University, Edinburgh, Scotland web site shows FLAPS (Flexible Appendage for Positioning and Stabilisation) for a fish-like propulsor with a tuna shaped vehicle picture with a foil attached to the end. Texas A&M University and Aeroprobe Corp. have shown work on a shape memory alloy test platform which is not a vehicle but resembles a fish. They articulate the aft 15-20% of the foil shaped body. The University of New Mexico and Artificial Muscles Research Institute are researching ion exchange polymer metal composite as biomimetic actuators. They show an autonomous "robotic swimmer" which has the form of a small boat with a tadpole like beam tail which oscillates. It is very small (6 inches) with an oscillating section roughly 20% of the total length.